[3] Capper was employed on home service for the next ten years and whilst serving as regimental adjutant[4] was promoted to captain on 22 April 1891,[5] attending the Staff College at Camberley from 1896 to 1897 before being transferred with his unit to India.

[6] Three years later he was again in action as an advisor to an Egyptian unit of the Anglo-Egyptian army under Horatio Kitchener which travelled down the Nile in the final campaign of the Mahdist War.

[2] He came into contact with numerous important figures of the First World War through this work, including Douglas Haig, with whom he did not get on, and Hubert Gough, who admired his "spirit of self-sacrifice and duty, instead of the idea of playing for safety and seeking only to avoid getting into trouble".

[28] He relinquished command of the brigade in February 1914 and briefly returned to Ireland, in the aftermath of the Curragh incident, to support his friend Hubert Gough.

[6] On 6 October his 7th Division, comprising Harold Ruggles-Brise's 20th, Herbert Watts's 21st, and Sydney Lawford's 22nd infantry brigades and supporting elements, arrived at Zeebrugge just as the German forces began to push into that area as part of the "Race for the Sea".

[33][34] Remaining on the front lines during the winter of 1914–1915, Capper's men held the German advance and were given some respite in early 1915 with the arrival of Territorial Force (TF) units.

It was during one of these rest periods that Capper was seriously wounded when in April 1915 he was struck in the shoulder by shrapnel from a "Jam-tin bomb" during a demonstration of improvised grenades being held behind the lines.

Advancing on 26 September against furious German opposition, the 7th Division was held up several times and Capper visited the frontline to view the enemy for himself from the captured trenches.

Urging his men into a final assault, Capper stayed behind to view the field and was struck by a sniper's bullet fired from houses along the line of advance which were thought to have been abandoned.

[6] The assault failed and Capper was discovered by his retreating units and taken to Number 6 Casualty Clearing Station at Lillers to the rear of British lines[6] personally by Captain O'Reilly, a medical officer.

His collected papers were donated to King's College London in 1971, where they are still available to researchers and contain a wide selection of primary materials concerning the warfare of the early twentieth century.